Ir films were deposited on molybdenum substrates by MOCVD using iridium tri-acetylacetonate as precursors. The effects of deposition temperature and oxygen on deposition effectiveness of iridium were discussed. The relationship between the deposition rate and the deposition temperature does not accord with Arrhenius formula; however, there exists a parabola relation between them. The deposition rate of iridium will reach maximum at 750 oC. The deposition temperature greatly affects the film properties. The component, the surface morphology and the structure of Ir films will be influenced by the addition of oxygen